The invention lies in the field of loudspeakers. The invention relates to loudspeaker drive units and is particularly concerned with compound loudspeaker drive units in which separate diaphragms are provided for reproduction of different audio frequency ranges.
British Patent No. 2,236,929, corresponding to U.S. Pat. No. 5,548,647 to Fincham, describes a compound loudspeaker drive unit including a low-frequency unit having a conical diaphragm and a high-frequency unit located in or adjacent to the neck of the low-frequency conical diaphragm such that the acoustic centers of the two units are substantially coincident. The radiation pattern or directivity of the low-frequency drive unit is determined, inter alia, by the form of the low-frequency diaphragm. With the high-frequency drive unit positioned adjacent to the neck of the low-frequency diaphragm, the form of the low-frequency diaphragm imposes its directivity upon the radiation pattern or directivity of the high-frequency unit. Consequently, at frequencies at which both drive units contribute significant sound output, both drive units have substantially similar patterns of radiation or directivity. As a result, the relative sound contributions from the two drive units as perceived by a listener are substantially unaffected by the listener being positioned at an off-axis position.
In the Fincham compound loudspeaker drive unit, the conical diaphragm of the low-frequency unit has a flexible rolled surround that is secured to the front rim of the chassis. The rolled surround constitutes a discontinuity. The use of a rolled surround, of substantially semicircular shape, has been a conventional practice for permitting the diaphragm of a low-frequency drive unit to perform the required movements. Examples of such diaphragm surrounds are to be found, for example, in U.S. Pat. No. 3,997,023 to White, U.S. Pat. No. 5,418,337 to Schreiber, U.S. Pat. No. 5,687,247 to Proni, U.S. Pat. No. 5,949,898 to Proni, and U.S. Pat. No. 6,173,065 to Lin.
The diaphragm surround plays an important part in the functioning of the loudspeaker drive unit.
In the case of a compound loudspeaker drive unit as described in Fincham, one of the problems that arises is the occurrence of diffraction from the high-frequency drive unit occurring at the roll. Such diffraction has an adverse effect on the frequency response at high frequencies. The diffraction is caused by the obstruction that the roll constitutes.
British Patent No. 2,315,185, corresponding to U.S. Pat. No. 6,219,432 to Fryer et al. (hereinafter xe2x80x9cFryerxe2x80x9d), describes loudspeaker drive units that include a surround not of the conventional rolled form. Fryer discloses various configurations for the surround 4, 4A, 4B, 4C, 4D, 30, 30xe2x80x2. In all of the configurations, the surround has a periphery spaced apart from the periphery of the chassis 3 in an axial direction of the speaker. See Fryer at FIGS. 1 to 6, 8, and 9. Thus, the surround 4, 4A, 4B, 4C, 4D, 30, 30xe2x80x2 has a sharp transition at the connection point to the chassis 3. Fryer is not related to a compound loudspeaker drive unit. There is a particular problem with diffraction when one has a compound loudspeaker drive unit with a high-frequency drive unit, i.e., a tweeter, positioned centrally within the diaphragm of the lower frequency drive unit.
British Patent 1,563,511 describes a diaphragm for an electro-acoustic transducer that can be used as a single speaker over an entire frequency range. This loudspeaker has a conical diaphragm 1 that sharply curves to join the supporting basket 11 at the basket""s periphery through a cone support ring 12.
U.S. Pat. No. 5,608,810 to Hall discloses embodiments for woofer (low-frequency) single speaker unit or a midrange single speaker unit. In the woofer unit, a mastic band 59 connects the curved member 12 to a three-section surround 50 (52, 54, 56), which is, in turn, connected at the groove 57 of the plate 20. The curved member 12 has an angle-shaped periphery 14 that is connected to the end portion 54 of the surround 50. In the midrange unit, a mastic band 80 connects the curved member 12 to a surround 78, which is, in turn, connected at the groove 72 of the plate 70. The curved member 12 in the midrange unit, like the woofer unit, has an angle-shaped periphery 14 that is connected to the surround 78 by the mastic band 80. Thus, between the curved member 12 and the surround 50, 78 is a sharp transition.
It is accordingly an object of the invention to provide loudspeaker drive units that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that reduces and, indeed, minimizes, such diffraction in a compound loudspeaker drive unit. As such, the invention produces an improved frequency response at high frequencies.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a mid-frequency loudspeaker drive unit, including a substantially conical diaphragm having a forward periphery and a surround connected to and extending from the forward periphery of the diaphragm to form a substantially smooth transition from the diaphragm to the surround, the diaphragm and the surround presenting a substantially smoothly continuous outwardly facing surface. Preferably, the transition is entirely smooth and the diaphragm and the surround present an entirely smoothly continuous outwardly facing surface.
With the objects of the invention in view, there is also provided a compound loudspeaker drive unit, including a mid-frequency drive unit having a substantially conical diaphragm with a center axis and a forward periphery, and a high-frequency drive unit coaxially disposed within the diaphragm, a chassis encompassing the mid-frequency drive unit, the mid-frequency drive unit having a surround connected to and extending from the forward periphery of the diaphragm and secured to the chassis to form a substantially smooth transition from the diaphragm to the surround, the diaphragm and the surround presenting a substantially smoothly continuous outwardly facing surface.
In accordance with the invention, a compound loudspeaker drive unit includes the mid-frequency drive unit of the invention and a high-frequency drive unit where the diaphragm of the high-frequency drive unit is located centrally within the diaphragm of the mid-frequency drive unit, a flat surround having a smooth continuation of the profile of the diaphragm.
By having a smooth transition from diaphragm to surround, without any discontinuity, and with a smoothly continuous surface, the problem of diffraction from the high-frequency drive unit is minimized. It is possible to use a smoothly continuous surround for a mid-frequency diaphragm because such a diaphragm undergoes less displacement than in the case of a diaphragm of a low-frequency or bass drive unit. In practice, the compound mid-frequency/high-frequency drive unit would be used with a dedicated bass unit in a loudspeaker cabinet.
References herein to xe2x80x9cmid-frequencyxe2x80x9d are intended to mean frequencies in the range of approximately 300 Hz to 6 KHz for a 6-inch diameter diaphragm, with appropriate modifications of that range for diaphragms of larger or smaller dimensions.
In accordance with another feature of the invention, the diaphragm is of random copolymer polypropylene.
In accordance with a further feature of the invention, the surround is of a polypropylene elastomer.
In accordance with an added feature of the invention, the diaphragm has a given thickness and the surround has a thickness ranging between the given thickness and 125% of the given thickness.
In accordance with an additional feature of the invention, the diaphragm has a given thickness and the surround has a thickness substantially equal to the given thickness.
In accordance with yet another feature of the invention, the diaphragm has an outer edge surface having given thickness and the surround has an interior surface having a thickness substantially equal to the given thickness.
In accordance with yet a further feature of the invention, the surround has an exterior surface having a thickness greater than the given thickness.
In accordance with a concomitant feature of the invention, the surround has an exterior surface having a thickness approximately 125% of the given thickness.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in loudspeaker drive units, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.